The present invention relates to an optical disk device for recording and reproducing data on and from an optical disk by an optical pickup, and a method for adjusting an emission current of a laser in an optical disk device.
As optical disk devices, devices for CD-ROMs, CD-R/RWs, and DVDs have already been made practicable, and these are actively applied to various fields and developed for higher performance. Particularly, recently, along with rapid market expansion of personal computers, the diffusion ratio thereof in the form installed in personal computers has also increased.
FIG. 10 is a block diagram of a pickup control part of an optical disk device.
Operations of a pickup control part according to prior arts are described with reference to FIG. 10. In FIG. 10, the pickup module 2 comprises a spindle motor 3 for rotating an optical disk 1, an optical pickup 4 for recording and reproducing data signals of the optical disk 1, and a feed part 6 for moving a carriage 5 on which the optical pickup 4 is mounted in the radius direction of the optical disk 1. The feed part 6 comprises a feed motor 7, a gear (not shown), and a screw shaft (not shown), etc., and is constructed so that the carriage 5 moves between the inner circumference and the outer circumference of the optical disk 1 when the feed motor 7 is rotated.
An analog signal processing part 8 generates a focus error signal and a tracking error signal on the basis of a signal output from an optical sensor (not shown) inside the optical pickup 4 within the carriage 5 provided inside the pickup module 2, and outputs the signals to the servo processing part 9.
The focus error signal shows deviation between a light beam spot outputted from an objective lens (not shown) provided in the optical pickup 4 and the recording surface of the optical disk 1 in the focal direction. The tracking error signal shows deviation between the light spot and the data track of the optical disk 1 in the optical disk radius direction. The analog signal processing part 8 generates a lens position signal showing the relative positional relationship between the objective lens and the carriage 5 by extracting the low-band components of the tracking error signal, and outputs the signal to the motor drive part 10.
The servo processing part 9 comprises an ON/OFF circuit, an operation circuit, a filter circuit, and an amplifier circuit, etc., focus/tracking-controls the objective lens so that the light beam spot follows the data track of the optical disk 1, and furthermore, performs feed-control so that the objective lens maintains a roughly neutral- position by using the low-band components of the tracking error signal.
The digital signal processing part 11 comprises a data slicer, a data PLL circuit, a jitter measuring circuit, an error correction part, a modulating/demodulating part, a buffer memory, and a laser control part, etc., and transfers signals to the host (HOST in the figure) side as effective data.
In recording operations, data transmitted from the host is modulated by the digital signal processing part 11, a predetermined current is supplied to a laser light source (not shown) inside the optical pickup 4 via the laser drive part 12 by the laser control part to make the laser light source emit light in a pulsed manner, and performs recording on the data track of the optical disk 1. The controller 13 controls the entirety of the servo part thus constructed.
An example of a method for controlling the recording power in the optical disk device is described in Japanese Unexamined Patent Publication No. 2000-30276.
In the case of a medium for both recording and reproduction like a CD-RW and a DVD-RW, for forming bits, the recording emission waveform like the waveform of the recording emission intensity of FIG. 6 is formed. This recording emission waveform forms bits by repeating rapid-heating and rapid-cooling on a medium by repeating high power and low power light beams. Namely, with respect to an erase level for erasing recorded data, a peak level at a higher emission intensity level and a bottom level at a lower emission intensity level are alternately formed.
In order to realize this recording emission waveform, a current pattern to be supplied to the laser light source is shown in FIG. 7. A current to be supplied for obtaining bottom level emission intensity is a bottom current (iBT), and for obtaining erase level emission intensity, a current obtained by adding an erase current (iER) to the bottom current (iBT) is supplied. Furthermore, in order to obtain peak level emission intensity, a current further added with a peak current (iPK) is supplied.
The construction of D/A converters to be used for generating these emission currents is shown in FIG. 8. The D/A converter for generating a bottom current (iBT) is a bottom DAC, the D/A converter for generating an erase current (iER) is an erase DAC, and the D/A converter for generating a peak current (iPK) is a peak DAC. To obtain the bottom level emission intensity by currents generated by these D/A converters, only the bottom current (iBT) is supplied to the laser light source. To obtain the erase level emission intensity, a current being the sum of the bottom current (iBT) and the erase current (iER) is supplied to the laser light source. To obtain the peak level emission intensity, a current being the sum of the bottom current (iBT), the erase current (iER), and the peak current (iPK) is supplied to the laser light source.
The relationship between the current flowing in the laser light source and the emission intensity of the laser light source changes depending on the temperature of the laser due to influences from the laser's own heating and the ambient temperature. At a starting time of recording, the temperature is low, so that the threshold as the minimum current value necessary for emission is low, and the inclination of the increase in the emission intensity according to an increase in current is steep, however, during recording, due to an increase in temperature of the laser, the threshold becomes higher and the inclination of the emission intensity with respect to an increase in current becomes smaller. Therefore, in order to obtain desired emission intensity, adjustment of the current according to the temperature change of the laser becomes necessary.
For this current adjustment, it is not possible to directly detect the bottom level change, so that erase power of the emission intensity is detected, and on the basis of this result, an estimate value of the bottom level change is determined, and according to this, the bottom current (iBT) is adjusted. However, in this method, the bottom level adjustment is always based on the estimate value from the erase power of the emission intensity, so that this method cannot cope with a case where an unexpected source of change occurs, and accuracy is not sufficient. Therefore, the emission intensity level cannot be properly maintained, and the bottom level scatters and harmfully influences the recording performance, resulting in inaccurate data recording.